From 6b297cd64627a383ccb8d2d5a2ad736118a014ed Mon Sep 17 00:00:00 2001
From: Oran Agra <oran@redislabs.com>
Date: Sun, 24 Oct 2021 16:52:44 +0300
Subject: [PATCH] Improve errno reporting on fork and fopen rdbLoad failures
 (#9649)

I moved a bunch of stats in redisFork to be executed only on successful
fork, since they seem wrong to be done when it failed.
I guess when fork fails it does that immediately, no latency spike.
---
 src/rdb.c         |  2 +-
 src/replication.c |  2 +-
 src/scripting.c   |  2 +-
 src/server.c      | 11 +++++++----
 4 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/rdb.c b/src/rdb.c
index cb4351ea6..afdf57daf 100644
--- a/src/rdb.c
+++ b/src/rdb.c
@@ -3110,7 +3110,6 @@ int rdbSaveToSlavesSockets(rdbSaveInfo *rsi) {
         exitFromChild((retval == C_OK) ? 0 : 1);
     } else {
         /* Parent */
-        close(safe_to_exit_pipe);
         if (childpid == -1) {
             serverLog(LL_WARNING,"Can't save in background: fork: %s",
                 strerror(errno));
@@ -3141,6 +3140,7 @@ int rdbSaveToSlavesSockets(rdbSaveInfo *rsi) {
                 serverPanic("Unrecoverable error creating server.rdb_pipe_read file event.");
             }
         }
+        close(safe_to_exit_pipe);
         return (childpid == -1) ? C_ERR : C_OK;
     }
     return C_OK; /* Unreached. */
diff --git a/src/replication.c b/src/replication.c
index eb574d0ea..1c8836c02 100644
--- a/src/replication.c
+++ b/src/replication.c
@@ -1859,7 +1859,7 @@ void readSyncBulkPayload(connection *conn) {
         if (rdbLoad(server.rdb_filename,&rsi,RDBFLAGS_REPLICATION) != C_OK) {
             serverLog(LL_WARNING,
                 "Failed trying to load the MASTER synchronization "
-                "DB from disk");
+                "DB from disk: %s", strerror(errno));
             cancelReplicationHandshake(1);
             if (server.rdb_del_sync_files && allPersistenceDisabled()) {
                 serverLog(LL_NOTICE,"Removing the RDB file obtained from "
diff --git a/src/scripting.c b/src/scripting.c
index 374ebaf91..85504bdb0 100644
--- a/src/scripting.c
+++ b/src/scripting.c
@@ -2164,7 +2164,7 @@ int ldbStartSession(client *c) {
     if (ldb.forked) {
         pid_t cp = redisFork(CHILD_TYPE_LDB);
         if (cp == -1) {
-            addReplyError(c,"Fork() failed: can't run EVAL in debugging mode.");
+            addReplyErrorFormat(c,"Fork() failed: can't run EVAL in debugging mode: %s", strerror(errno));
             return 0;
         } else if (cp == 0) {
             /* Child. Let's ignore important signals handled by the parent. */
diff --git a/src/server.c b/src/server.c
index a064b8032..ee1b689a6 100644
--- a/src/server.c
+++ b/src/server.c
@@ -7405,14 +7405,17 @@ int redisFork(int purpose) {
         closeChildUnusedResourceAfterFork();
     } else {
         /* Parent */
+        if (childpid == -1) {
+            int fork_errno = errno;
+            if (isMutuallyExclusiveChildType(purpose)) closeChildInfoPipe();
+            errno = fork_errno;
+            return -1;
+        }
+
         server.stat_total_forks++;
         server.stat_fork_time = ustime()-start;
         server.stat_fork_rate = (double) zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024*1024*1024); /* GB per second. */
         latencyAddSampleIfNeeded("fork",server.stat_fork_time/1000);
-        if (childpid == -1) {
-            if (isMutuallyExclusiveChildType(purpose)) closeChildInfoPipe();
-            return -1;
-        }
 
         /* The child_pid and child_type are only for mutual exclusive children.
          * other child types should handle and store their pid's in dedicated variables.